Technical Field: The disclosure relates to the field of lockout devices for preventing the operation of a valve actuator and to the field of valve partial stroke test devices, which permit only a pre-determined extent of motion for the valve actuator.
Safety equipment in industrial process plants with piping and valve installations typically include emergency shutdown valves (hereinafter, also “ESD valves”), blow off valves and bypass valves to prevent pressure build up in upstream or downstream sections. These valves normally remain open or closed but are actuated quickly to isolate sections of piping to stop further flow or bypass the flow, for emergency safety reasons. Actuation on ESD valves use fail-close actuator that is biased to close the valve, which is normally maintained in an open position by pneumatic pressure. These valves automatically close by the spring action or by reserve pneumatic supply upon loss of line air pressure due to a pressure system failure or in response to an emergency shutdown command signal. Regulations mandate periodic testing of such safety-instrumented systems to ensure the valve and all control elements are fully operational in an emergency.
Partial stroke testing (hereinafter, also “PST”) devices fulfill this testing requirement without having to shut down the valve fully, which may disrupt or be detrimental to the normal process. A typical PST device is sandwiched between the valve and the actuator with a mechanical stop engaged to permit only a partial rotary motion of the valve operating member, or has a mechanical stop inserted into the translatory (meaning of, relating to, or involving uniform motion in one direction) path of the pneumatic actuator's piston rod, permitting only partial linear stroke.
However, the operational safety also demands lockout devices that are required to prevent the actuator from operating under the fluid power during maintenance and repairs. This typically is met by an additional device and often suffers from being singular in its orientation and point of action, whereas the actuators are invariably provided with an over travel adjustment to compensate for the valve's true closing position. The challenge has been to combine all such requirements with a compensating mechanism to match the locking position of the actuator to the valve's true closed position, after having adjusted the actuator's travel stops.
A solution to provide a combination device with its unique mechanism to compensate variability in the valve's true closing position and perform both of these said functions either by manual or remote operation, is the subject matter of this disclosure. Advantageous elaborations or embodiments of the disclosure are the objects of the present disclosure.
Some examples of prior art on lockout and partial stroke valve test apparatus are shown in FIG. 20, FIG. 21 and FIG. 22.
FIG. 20 shows a typical mechanical device that is fitted between the actuator and a rotary valve, the coupler shaft connects the valve's stem to the actuator's drive element. Rotary motion of the valve's drive member is restrained completely by a stopper bolt engaged in the device housing and the end of the stopper bolt locates into a hole or recess in the coupler shaft to lockout the rotary motion of the coupler and thereby the actuator and the valve. The device may further be locked out by engaging a lock pin through the housing and the stopper bolt and a padlock engaged into the lock pin. These device types are singular in their function as only a lockout apparatus and do not perform the partial stroke valve test.
FIG. 21 shows an arrangement to engage a stopper pin in the path of the actuator's piston rod or its extension thereof, to restrict the linear motion of the piston rod in a partial stroke valve test device. The spring return stroke is restricted to a small predetermined extent when the stopper pin is inserted in the device's housing, as the end face of the piston rod contacts the stopper pin after the partial stroke and is mechanically restrained by the pin from further motion.
FIG. 22 shows a partial stroke valve test device that is fitted between a rotary valve and the actuator with the device's coupler shaft adapted to connect the valve's stem to the actuator's drive member. The device typically has this coupler shaft keyed to a rotary member, segmented to provide a radial planar surface that bears on a cam stopper which when engaged, blocks the rotary motion of the segment and thereby the actuator and valve. The two extreme positions of the cam shaft select between the operation or test modes of the device. These device types are singular in their function as only a partial stroke valve test apparatus and do not lock out the actuator.